Various electronic-type and mechanical-type leak detectors have been suggested for use with storage tanks. For example, U.S. Pat. No. 2,531,159 discloses a float which raises upon leaking fluid filling a float vessel and causes tilt movement of a mercury switch to shut down a burner and simultaneously activate a warning light or alarm bell. U.S. Pat. No. 4,653,312 describes the use of a sight glass, color changes, pressure transducers and floats to detect leaks and a change in liquid level with an electronically linked alarm system.
A surface water detector has been sold by Retawmatic Corp. of New York City as Model 317A which includes an apertured housing with a water-expandible cartridge touching the surface to be surveyed. The cartridge absorbs water and swells up, pressing against an internal switch which upon such pressure starts an alarm. The cartridge after swelling may be dehydrated by dryers or heaters so that it shrinks and is reusable. Dorlen Products of Milwaukee, Wis., sells a surface water sensing alarm under the trademark Water Alert.RTM. which includes height adjustable 0-150 inch sensors, epoxy-encapsulated sensing and control circuitry and an electro-mechanical buzzer for alarm signalling.
The above sensors are relatively complex and expensive, have relatively high maintenance costs and are not very reliable. Further, they are not capable of accurately detecting a leak on a horizontal surface and also a vertical level of a liquid.